The ability of rotary impellers to both finely grind a solid material and evenly disperse it within a vehicle or carrier is important in a wide variety of industrial mixing applications. One example of such a mixing application includes, but is not limited to, mixing solid particles within a liquid slurry, e.g. mixing pigments within paint, sand within paint, sand within water, cement with water, and the like. In alternative examples, the mixing application may include mixing solid particles with a solid particle vehicle, i.e. evenly intermixing two powders. In each of these and other similar examples, the ability to finely grind the solid particles to a desired size and to evenly disperse these particles throughout the vehicle is important toward the effectiveness of the final mixture. Failure to provide a homogeneous final mixture could compromise the integrity of the product and prevent it from functioning properly.
One common operation to mix the solid particles within a vehicle is by an impeller affixed to a rotatable shaft. Referring to FIGS. 1 and 2, a typical impeller 80 generally comprises a flat metal disk 82 having a plurality of vanes or blades 84 extending from its edge and a plurality of grooves 81 between each blade 84. The impeller 80 is adapted to rotate with a rotatable shaft 83 such that the blades 84 and grooves 81 break apart solid particles within a slurry or liquid suspension and/or intermix the solid particles within a vehicle. The action of rotating the blades 84 and grooves 81 also creates a particle flow that disperses the particles relatively evenly throughout the vehicle. Dispersion is further facilitated by a bend slightly upward or downward of each blade 84, relative to the plane of the disk, such that particles flowing along the surface of the disk will be guided below or above the disk. Thus, the bend in the blade causes a vertical particle flow within the vehicle.
A common disadvantage of this type of impeller, however, is severe abrasion. The speed of rotation of the impeller, often rotated at a tangential velocity of 3500-6000 ft/min, increases the friction between the impeller and the slurry. Accordingly, the blades of the impeller quickly erode, especially if used to mix liquids having a high viscosity or abrasive solids suspended therein. Particles of metal may also break away from the impeller and become suspended within the liquid that is being mixed, thereby, contaminating the mixture. Thus, the impeller must be replaced frequently so as to maintain optimal efficiency and not contaminate the slurries. Replacement of each impeller causes a certain amount of down-time for the task at hand and increases the amount of time necessary to completely mix a slurry.
U.S. Pat. No. 4,171,166 (“the '166 patent”) and U.S. Pat. No. 5,201,635 (“the '635 patent) set forth a solution to the breakdown of the metallic impeller by providing a polymer-based, disc-like impeller. Specifically, the polymeric impeller contains a plurality of radially extending grooves on each planar face. Upon rotation of the impeller, these grooves create turbulent flow within the liquid vehicle, thereby, dispersing the solid particles throughout the slurry.
The grooves of the '166 and '635 patents, however, are limited in their ability to fully grind the solid material in the slurry. As a result, a greater amount of time is needed for these impellers to grind the solid material and to evenly dispersed it within the liquid vehicle. Greater processing time leads to increased costs associated with preparing the slurry. These increased costs are especially prevalent with viscous slurries and/or hard, dense, solid materials. As such, these impellers are not cheaply applicable for grinding and mixing these types of mixing applications.
Based on the foregoing, there is a need in the art for an apparatus providing an impeller for mixing solids within a vehicle with an improved ability to grind and disperse solid materials therein. As such, there is a need in the art for an impeller that improves the cost and productivity associated with grinding and evenly dispersing solid material within a vehicle, especially with high viscosity slurries and/or vehicle or carriers with hard, dense, solid particles.
The present invention addresses the foregoing needs.